7336

• UCREFRP Catalog Number: 7336
• Author: Valdez, R. A. and B. C. Nilson.
• Title: Radiotelemetry as a Means of Assessing Movement and Habitat Selection of Humpback Chub.
• USFW Year: 1982.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: YES

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area or the transmitter malfunctioned. Failure to locate fish through
searches outside of Black Rocks suggests the latter.

Based on these radiotelemetry data, humpback chub in Black Rocks
exhibit little movement from this restricted habitat from May .to August.
The maximum monitoring period of 93 days for three of the transmitters
indicates that these reached their theoretical life expectancy. Humpback
chub tagged with serially-numbered Carlin tags also exhibited little
movement, but over a greater period of time (maximum of 434 days).
Average movement per fish for the 16 recaptures was 1.63 km with a range
of 0-23.0 km (Table 2).

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This investigation indicates that humpback chub rarely leave
restricted habitats in the upper Colorado River such as Black Rocks.
They tend to reside throughout the year within very limited reaches of
river that are relatively deep, swift and rocky.

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Movement by a radio-tagged fish in Black Rocks is demonstrated by
one male monitored periodically for 67 days (Figure 1). The fish spent
26 days near the release site; 2 days enroute to the original capture
site, about 2 km upstream; and the remaining 39 days of monitoring in the
area of original capture. The behavior of this fish and that of two
others that returned to their original capture site suggests a homing
behavior by the species that closely ties individuals with specific
areas of the river.

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Patterned diurnal and nocturnal movements were also observed in
these radio-tagged fish (Figure 2). The fish generally occupied depths
of less than 5 m during dawn (0600-0800 h) and evening (2000-2300 h), and
5-7 m in midmorning (0800-1100 h)~afternoon (1700-1800 h). At midday
(1100-1700 h) and midnight (2300-0600 h), the chubs seemed to. occupy
waters deeper than about 7 m. This behavior was difficult to monitor
since reception was weak from depths greater than 6 m. The radio-tagged
fish often situated themselves in eddies or pools behind submerged or
emergent rocks and remained there for hours, occasionally straying into
the nearby current. When the fish were positioned near steep rock walls,
they appeared to remain close to midwater ledges and made occasional
forays into or across the swift midchannel current. Nearly all of the
radio-tagged fish demonstrated an ability to traverse swift (7 fps) and
deep (18 m) water, but preferred to position themselves in the more quiet
areas.

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Habitat Use

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A total of 85 observations (measurements of depth, velocity and sub-
strate) were made on the eight humpback chub during the monitoring
period. These data are compared with those taken during captures of 136
adult chub by electrofishing and entanglement nets.

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